CMB?

1. Espectro de la RCF

2. Anisotropías de la RCF

CMB anisotropy

Anisotropies

T(θ,φ), Q(θ,φ), U(θ,φ), V(θ,φ)

X=T,E,B

X(θ,φ)=Σlm almX Ys

lm(θ,φ)

spherical harmonics

s=0 for T, 2 for Q and U

E and B modes have opposite parity

Angular power spectrum

T(θ,φ), Q(θ,φ), U(θ,φ), V(θ,φ)

aXlm, X=T,E,B

Cl=Σm [(almX)(alm

Y)*]/(2l+1)

spherical harmonics

informationcompression

Use Ripples in CMB to Measure Composition of the Universe

• The Basic Idea: Hit it and listen to the cosmic sound.– Analogy: Brass and ceramic can be discriminated by hitting them and

listening to the sound created by them.– We can use sound waves to determine composition.

• When CMB was emitted the Universe was a dense and hot soup of photons, electrons, protons, Helium nuclei, and dark matter particles.– Ripples in CMB propagate in the cosmic soup: the pattern of the ripples,

the cosmic sound wave, can be used to determine composition of the Universe!

How do we “hear” the cosmic sound from this?

• metric perturbations

•Decomposition into scalar, vector and tensor components

Linear cosmological perturbation theory

The cartoon

• At early times the universe was hot, dense and ionized. Photons and matter were tightly coupled by Thomson scattering.– Short m.f.p. allows fluid approximation: baryon-photon fluid

• Initial fluctuations in density and gravitational potential drive acoustic waves in the fluid: compressions and rarefactions.

• A sudden “recombination” decouples the radiation and matter, giving us a snapshot of the fluid at “last scattering”.

[harmonic wave]

Approximate Equation System in the Strong Coupling Regime

SOUND WAVE!

Cosmic Sound Wave!

• It is the nature of things that they are ties to each other. —Chuang-tzu (300BC)

It is the nature of things that they are ties to each other. —Chuang-tzu (300BC)